1. Field of the Invention
The present invention relates to sonar systems and more particularly to electronic means for steering sonar beams in such systems.
2. Description of the Prior Art
Ship-mounted sonar systems sometimes provide acoustic beams essentially only in a horizontal plane. Such systems are satisfactory for acoustic energy received along a direct path or from a convergence zone. However such systems are not satisfactory for situations where it is desired to receive energy reflected from the ocean bottom. Sonar systems capable of responding to such "bottom bounce" have been developed wherein provisions are made for depressing the acoustic beams. However such systems are more complicated than those intended only for horizontal transmission and reception.
Typically, marine sonar systems employ a hydrophone array in which the individual elements in the array are combined with proper delays in order to form an acoustic beam. A square array might be used, for example, where inter-element delays can be provided to steer the beam in a horizontal or vertical plane. If a beam is to be formed in one plane only (e.g., in the horizontal plane), the elements in the opposite (vertical) plane are combined without inter-element delays, preserving only the ability to steer the beam in the first (horizontal) plane by introducing delays between elements in that plane.
In some prior art systems, capability of steering the beam in either plane is achieved by complex means for controlling the delays asociated with each element. Such systems permit vertical steering to optimally steer the beam for bottom bounce as well as direct path and convergence zone operation, but this flexibility is achieved at the expense of considerable complexity in the form of individual cables, hull penetration and front end electronics as well as increased data to be processed by the beamformer.
In summary, prior art simple sonars sacrifice bottom bounce capability, whereas improved sonar systems capable of bottom bounce operation are excessively complex.
The present invention overcomes the aforementioned dual problem by providing bottom bounce capability without substantial sacrifice of direct path or convergence zone capability and without a major increase in complexity.